In recent years, object oriented programming has become the standard programming paradigm. In object oriented programming, the world is modeled in terms of objects. An object is a record combined with the procedures and functions that manipulate it. All objects in an object class have the same fields ("attributes"), and are manipulated by the same procedures and functions ("methods"). An object is said to be an "instance" of the object class to which it belongs.
Sometimes an application requires the use of object classes that are similar, but not identical. For example, the object classes used to model both dolphins and dogs might include the attributes of nose, mouth, length and age. However, the dog object class may require a hair color attribute, while the dolphin object class requires a fin size attribute.